A manufacturing process of a semiconductor device includes various process steps that perform various heat treatments, such as an oxidation treatment, a diffusion treatment, a CVD treatment, and an annealing treatment, to a process object, e.g., a semiconductor wafer. A vertical heat treatment system capable of heat-treating plural wafers at one time has been used as one of heat treatment systems for performing the foregoing process steps.
The vertical heat treatment system includes: a heat treatment furnace having a furnace throat in its lower end; a lid that hermetically closes the furnace throat; a holder (also referred to as “wafer boat”) disposed on the lid to hold plural wafers at predetermined vertical intervals via ring-shaped support plates; an elevating mechanism that vertically moves the lid to load and unload into and from the heat treatment furnace; and a transfer mechanism that transfers wafers between the holder and a container (also referred to as “carrier” or “cassette”) for holding therein plural wafers at predetermined intervals. The transfer mechanism is provided with plural substrate support devices (also referred to as “forks”) spaced at predetermined intervals. The ring-shaped support plate is employed for suppressing or preventing slippage (i.e., crystal defect) which may occur in the peripheral portion of a wafer during a heat treatment at a high temperature.
JP5-13547A discloses a vertical heat treatment system provided with a push-up type transfer mechanism (hereinafter referred to as “transfer mechanism A”) including a substrate support device 50 for conveyance and a substrate support device 51 for pushing-up operation, which is shown FIG. 12. The substrate support device 50 comprises a plate-shaped member having an upper surface for supporting thereon the lower surface of a wafer W. The substrate support device 51 for pushing-up operation comprises a plate-shaped member provided thereon with three supporting pins 52 each having an upper surface for supporting thereon the lower surface of a wafer W.
When transferring a wafer to a holder 9, the substrate support device 50 for conveyance supporting a wafer W is at first positioned above a ring-shaped support plate 15 in the holder 9, while the substrate support device 51 for pushing-up operation is positioned below the ring-shaped support plate 15 (FIG. 12(a)). Then, the substrate support device 51 for pushing-up operation is elevated to raise the wafer W from the substrate support device 50 for conveyance, and the substrate support device 50 for conveyance is withdrawn from the holder 9 while the wafer W is kept raised by the substrate support device 51 (FIG. 12(b)). Then, the substrate support device 51 for pushing-up operation is lowered to place the wafer W onto the ring-shaped support plate 15, and thereafter the substrate support device 51 for pushing-up operation is withdrawn from the holder 9 (FIG. 12(c)). In this manner, the transferring operation of one wafer is completed.
JP2003-338531A discloses a vertical heat treatment system provided with a transfer mechanism (hereinafter referred to as “transfer mechanism B”) configured to support a substrate on the lower side of a fork (i.e., a substrate support device) in such a manner that the substrate is suspended from the fork. The transfer mechanism has plural engagement members each projecting downward from the folk and having an L-shaped cross section. The lower surface of a wafer is supported, at a peripheral portion thereof, on an upper surface of a horizontally-extending portion of each L-shaped engagement member. The respective engagement members are driven by an actuator to move between a wafer support position where the engagement members support a wafer, and a wafer release position where the respective engagement members are moved outside the outer peripheral edge of the wafer to release the wafer.
Both of the foregoing transfer mechanisms A and B transfer wafers only one by one. Thus, a long time is needed for wafer transfer operation, which inhibits improvement of throughput. Since the transfer mechanism has a large thickness (i.e., the size measured in the height direction) due to its structure, the arrangement pitch of the ring-shaped support plates in the holder must be as large as, for example, 16 mm. Thus, the maximum number of wafers to be held (treated) in a holder of a predetermined size is about 50 at most, which also inhibits improvement of throughput. Meanwhile, in the transfer mechanism B, all the engagement members disposed on the distal end side and the proximal end side of the fork are movable, and thus a complicated structure is added to the fork. Therefore, the height of the fork is undesirably increased, which makes it difficult to reduce the arrangement pitch of the ring-shaped support plates in the holder.